French Unexamined Patent Application No. 2 644 866 discloses a drive mechanism for accessory assemblies of a reciprocating internal combustion engine having a switchable planetary transmission. The planetary transmission is positioned concentrically to the crankshaft and includes a planetary gear carrier attached to the crankshaft, planet gears, a ring gear that can be locked against an end shield using a braking device and a sun gear that is connected to a belt pulley. The sun gear is positioned in the end shield and can be connected to the planetary gear carrier via a one-way clutch.
Switchable planetary transmissions of this type are intended to provide adequate power to accessory assemblies, such as an air conditioner compressor and electric generator, at engine idling speeds without causing those assemblies to race at high engine speeds, which may cause damage. This makes it possible to guarantee the operation of the vehicle electrical system even if the accessory assembly size might be reduced. This is so even if an electrically heated windshield and an electrically heated (pre)-catalytic converter are needed in addition to the equipment now present. The latter is an important prerequisite in reducing pollutant emissions during a cold start.
However, the switchable planetary transmission described in French Unexamined Patent Application 2 644 866 has a large volume and poor efficiency, since it is difficult to lubricate. Because it is connected rigidly to the free end of the crankshaft, this planetary transmission is subjected to the latter's vibratory load, making it susceptible to failures and producing noise emissions.
A switchable planetary transmission whose drive provides damping of the torsional vibrations stemming from the crankshaft is known from German Patent Application No. 1 526 560. This damping is achieved by a combination of compression springs and rubber cushions that are arranged in the planetary gear carrier. However, this has no effect on radial or axial vibrations of the crankshaft end, but only on its tangential vibrations which, unlike radial and axial vibrations, can be corrected by torsional vibration isolators and vibration dampers.